1. Field of the Invention
The invention relates to a fuel supply apparatus for an internal combustion engine and, more particularly, to a fuel supply apparatus having a separation membrane that separates a material fuel into a high-octane fuel and a low-octane fuel.
2. Description of the Related Art
As an example of an art for separating a fuel (a fuel serving as a material fuel) using a separation membrane and supplying the separated fuels, having properties different from the material fuel, to an internal combustion engine is described in the Japanese Unexamined Patent Publication (Kokai) No. 5-312115. An apparatus of the ""115 publication separates gasoline in a gasoline tank into a fuel having a low-boiling point (a low-boiling fuel) and a fuel having a high-boiling point (a high-boiling fuel) by using a pervaporation membrane, and stores the obtained low-boiling fuel in a fuel tank. At the time of a startup of the engine or a cold operation thereof, the apparatus supplies the low-boiling fuel stored in the fuel tank to the engine. The apparatus of the publication performs the startup or cold operation of the engine by using the low-boiling fuel separated from the material fuel during operation of the engine, so as to improve the startup characteristic of the engine, and the property of the exhaust gas, during the cold operation.
Since the low-boiling fuel is separated from an ordinary gasoline in the apparatus of the ""115 publication mentioned above, the apparatus is able to obtain the low-boiling fuel from an ordinary gasoline without needing a separate supply of a low-boiling fuel, and can improve the startup characteristic of the engine and the property of the exhaust gas, during the cold operation, by using the low-boiling fuel.
However, although the apparatus of the aforementioned publication uses the low-boiling fuel separated from gasoline, the apparatus returns the fuel remaining, after separation of the low-boiling fuel, to the gasoline tank, and mixes it with the material fuel.
If a fuel containing a large amount of low-boiling components is separated (extracted) from a gasoline through the use of a separation membrane, the remnant fuel is a high-boiling fuel having a larger content of high-boiling components than the material fuel. However, with regard to the aforementioned apparatus, only the use of the low-boiling fuel for startup of the engine is taken into consideration, and the use of the high-boiling fuel is not considered at all.
Therefore, the high-boiling fuel produced by the separation membrane is not utilized, but is mixed with the material fuel in the gasoline tank. Furthermore, if a large amount of the low-boiling fuel is produced, the amount of the high-boiling fuel refluxed to the material fuel also becomes large, and therefore it is a conceivable that all the fuel in the gasoline tank will have an increased content of the high-boiling component. In the apparatus of the ""115 publication, however, the amount of the low-boiling fuel needed is smaller than the amount of fuel provided within the gasoline tank since the low-boiling fuel is used only at the time of startup of the engine or cold operation thereof. Therefore, the amount of the high-boiling fuel produced as a byproduct of the low-boiling fuel is small, and the boiling point of the fuel within the tank does not significantly change from the boiling point of the material fuel despite high-boiling fuel being mixed with the fuel within the gasoline tank.
That is, the apparatus of the ""115 publication uses only the low-boiling fuel, but does not effectively use the high-boiling fuel separated by consuming energy. About a half of the energy used for fuel separation is uselessly consumed. Furthermore, in the apparatus of the ""115 publication, the separated low-boiling fuel is used only at the time of startup of the engine or the time of cold operation, but is not used at the time of ordinary operation after warm-up of the engine. Therefore, there is a problem that the separated fuel is not effectively used.
In view of the aforementioned problem of the conventional art, it is an object of the invention to improve the performance of an engine or the property of exhaust gas and prevent useless consumption of energy for fuel separation, in a case where two kinds of fuels having different properties are separated from a material fuel through the use of a separation membrane, by selectively using the two fuels in accordance with the state of operation of the engine.
According to the present invention, there is provided a fuel supply apparatus for an internal combustion engine comprising: a separation membrane for separating a fuel supplied as a material fuel into a high-octane fuel containing a larger amount of a component of a high octane value than the material fuel and a low-octane fuel containing a larger amount of a component of a low octane value than the material fuel; and a high-octane fuel supply passage and a low-octane fuel supply passage that are independent from each other and that are capable of supplying the high-octane fuel and the low-octane fuel, after separation, respectively, separately to the internal combustion engine, the fuel supply apparatus for the internal combustion engine being characterized by supplying one or both of the high-octane fuel and the low-octane fuel to the internal combustion engine in accordance with an engine operation condition.
That is, in the present invention, the material fuel is separated into the high-octane fuel containing a large amount of a high-octane component and a low-octane fuel containing a low-octane component. Since one or both of the separated low-octane fuel and the separated high-octane fuel are supplied to the internal combustion engine in accordance with the engine operation condition, not only one of the separated fuels (e.g., the low-octane fuel) but also the other separated fuel (e.g., the high-octane fuel) is effectively used. Furthermore, since it becomes possible to change the octane value of fuel in accordance with the operation state of the engine, the engine performance, such as output or the like, and the property of the exhaust, are improved.
The separation membrane can be a type which allows components in the material fuel having octane values within a predetermined range to permeate through the membrane. Further, permeability control means for controlling the amount and/or property of the fuel composed of the components permeated through the membrane may be used. The permeability control means controls the operation condition of the membrane which affects the permeation of the fuel components through the membrane such as pressures on both sides of the membrane and the supply rate of the material fuel and temperature of the material fuel or the separation membrane.